A compact disk (hereinbelow referred to as CD) has been widely used as a recording medium in which continuous information such as music information is digitally recorded in the form of minute pits which can be optically detected. A CD-ROM (Compact Disk Read Only Memory) starts to be widely applied to record not only the music information but also digital information such as computer-use data since the CD has the big recording capacity and the good productivity. Hereinbelow the CD-ROM is also referred to as the CD for sake of convenience. The CDs are reproduced by an optical disk reproducing apparatus (CD player) which is used for reproduction only.
FIGS. 12 and 13 show the schematic signal format for use in the CD. As shown in FIG. 12, one frame 50a of a recording signal is composed of: (1) a frame synchronization signal 50b indicative of a head end of the frame; (2) a sub-code 50c indicative of an additional information for data; and (3) a data field 50d which is formed by adding 8-byte parity code to 24-byte data of main information. The 8-byte parity code is for correcting error upon detecting the error in the process. The data field 50d is formed based on an error detection and correction system into which non-completion type interleave which is referred to as CIRC (Cross Interleaved Reed Solomon Code) is incorporated.
As shown in FIG. 13, one sub-coding frame (hereinbelow referred to as sector) 51a is composed of 98 frames 50a. A sub-coding block 51c is composed of 98 sub-codes 50c of the respective frames 50a. The data of the sub-coding block 51c indicate the track number, which is referred to as a song number when the main information is the music information, and the absolute address on the disk.
The length of one sector is 13.3 ms which corresponds to 1/75 seconds. A sector number is expressed by the combination of "minutes": "second": "a number of 0 to 74 within one second", the sector number being indicative of the assigned number on the disk. The sector number indicates both time information and position information which respectively increase consecutively as the radial position on the disk becomes far away from the innermost portion.
FIG. 11 is a plan view showing the area arrangement on the CD. A disk 52 has a main information recorded area 52b and a TOC (Table Of Contents) area 52a. Main information such as music information and the sector numbers derived from the sub-code are recorded in the main information recorded area 52b. Additional information is recorded in the TOC area 52a, the additional information being derived from the sub-code with regard to each main information recorded in the main information recorded area 52b. The additional information includes each track number, the recording start sector number for each track, information for identifying whether the main information recorded in the track is audio information or computer-use data.
When the CD player is loaded with the CD having the above-mentioned format, the sub-code information is first read out of the TOC area 52a. According to the reading, the respective numbers of the main information (corresponding to the song numbers for the music information), the recording start sector number for each main information, the kinds (audio or data) of the recorded information are identified. When received the reproduction instruction, the information of the TOC area 52a is compared with the sector number derived from the sub-code of the main information recorded area 52b. According to this comparison, the reproducing operation with respect to a target track is immediately carried out with the access operation combined.
The information is recorded in the CD based on the CLV (Constant Linear Velocity) method. Therefore, the recording density is constant over the whole disk, thereby being preferable for improving the recording capacity of the CD. The CD player rotates the CD at the constant linear velocity such that the interval between the frame synchronization signals has a reference length for example. The frame synchronization signals are derived from the reproduced signal which is reproduced from the recorded information in the CD based on the CLV method employing the above-mentioned signal format.
In contrast, when a variety of information such as music information and computer-use data are recorded and reproduced with respect to a rewritable disk such as a magneto-optical disk which has been recently developed, it is hoped to provide a compatible disk recording and reproduction apparatus which has a common reproduction system to both the CD and the magneto-optical disk.
such case, especially in an initial disk wherein no information is recorded, (1) the access operation with respect to an arbitrary sector and (2) some means for carrying out the CLV control with respect to the main information unrecorded area are required prior to the recording. This is because there exists no absolute address, in the initial disk information, using the above-mentioned sub-code and no frame synchronization signal used for the CLV control.
As shown in FIG. 14, in order to record an absolute address information which is equivalent to the absolute, address information derived from the sub-code, there is proposed the following method wherein a series of information such as the absolute address information and error detection and correction code is subjected to "biphase-mark" modulation and thereafter a guide groove 52c (indicated as hatched lines for sake of convenience), which is formed beforehand (pre-recorded) as a pre-recorded information in a radial direction of the disk at a predetermined interval, is deviated to an outer side or to inner side of a radial direction in response to the respective modulated bits "1" or "0" (see U.S. Pat. No. 4,907,216). The information reproducing apparatus can carry out the CLV control and the absolute address information detection with respect to the the main information recorded area 52b of the rewritable recording medium such as the magneto-optical disk when the above-mentioned recording method is adopted.
FIG. 9 is a block diagram showing an example of the information reproducing apparatus using the magneto-optical disk which is compatible with the above-mentioned CD format. A magneto-optical disk 61 is supported by a spindle motor 62 so as to rotate. A signal reproduced by an optical head 64 is amplified by a reproducing amplifier 65. A magneto-optical signal (Ps), which is changed into a binary condition, is outputted to both a first clock generating circuit 68 and a reproduced data processing circuit 74.
The pre-recorded information is outputted to a pre-recorded information detecting circuit 66. The pre-recorded information detecting circuit 66 is composed of a band-pass filter and a PLL for example, wherein a synchronized clock is generated by the PLL with respect to the pro-recorded information of the reproduced signal which is extracted by the band-pass filter. The clock synchronized with the pre-recorded information which is formed by the biphase-mark modulation of the absolute address is outputted to a CLV controlling circuit 63.
The CLV controlling circuit 63 compares the frequency of the synchronized clock of the pre-recorded information detecting circuit 66 with a reference frequency, within the circuit 63, which is synchronized with a clock of a second clock generating circuit 70 (later described). The CLV controlling circuit 63 controls the spindle motor 62 in response to the frequency difference, thereby causing to carry out the CLV control with accuracy with respect to the unrecorded area where no main information is recorded.
The pre-recorded information of the reproduced signal which is extracted by the pre-recorded information detecting circuit 66 is supplied to an address detecting circuit 67 which is composed of a biphase-mark demodulation, circuit and an address decoder circuit. The address detecting circuit 67 carries out the biphase-mark demodulation with respect to the pre-recorded information which is extracted by the pre recorded information detecting circuit The demodulated pre-recorded information is decoded into position information on the disk, i.e., the absolute address (equal to the sector) by the address decoder circuit so as to be supplied to a controller 75.
A reproduced data processing circuit 74 carries out the removing of the frame synchronization signal from the bynary magneto-optical signal (Ps) of the reproduced signal from the reproducing amplifier 65 and the EFM (Eight to Fourteen Modulation) demodulation so as to remove the sub-code information. Thus removed signals are supplied to the controller 75. The reproduced data processing circuit 74 also writes the main information and the parity as the reproduced data in a memory 73 so as to carry out the error correcting operation based on the CIRC.
The controller 75 receives a reproducing instruction from a host device through a terminal 79 and an interface 78. The controller 75 has an access function. According to the access function, the controller 75 identifies where the optical head 64 is located on the disk upon reception of the absolute address information from the address detecting circuit 67 and the optical head is moved to a target position by use of an optical head moving mechanism (not shown). The controller 75 also identifies the sub-code information of the reproduced data processing circuit 74.
When considering the clock system which processes the reproduced data, a clock synchronized with the reproducing signal should be used for writing the reproduced signal which has been subjected to the EFM demodulation. The EFM demodulated data are written in the memory 73 in the following manner: (1) the memory address is supplied to the memory 73 through a switching device 72, the memory address being generated by a write address generating circuit 69 resposive to the clock of a first clock generating circuit 68; and (2) the EFM demodulated data are written in accordance with the supplied memory address in a predetermined sequence.
In contrast, as to the reading operation from the memory 73, the data are read out from the memory 73 in the following manner: (1) the memory address is supplied to the memory 73 through the switching device 72, the memory address being generated by a read address generating circuit 71 resposive to a reference clock of a second clock generating circuit 70; and (2) the data are written in accordance with the supplied memory address in a predetermined sequence.
In such case, the data corresponding to the main data of FIG. 13 is converted into the analog audio information so as to output through a terminal 77 or so as to output to the host device which is connected with the terminal 79 through the interface 78. The address generating sequence of the write address generating circuit 69 is not the same as that of the read address generating circuit 71. The respective address generating circuits 69 and 71 also carry the deinterleave by which the data, arranged based on the interleave during the recording of the disk, are relocated as the original data.
The continuous reproducing is carried out by controlling the spindle motor 62 in a minute manner such that the period of the frame synchronization signal of the reproduced signal coincides with the reference period of the second clock generating circuit 70 system, thereby avoiding the surplus and shortage of the recording capacity of the limitative memory 73 for the data writing and the data reading to and from the memory 73. When the surplus and shortage of the memory 73 occurs in the recording capacity, setting operation is carried out, in order to avoid the destruction of the data which are already written, such that the read address is set as the write address when it is detected that the difference between the write address and the read address exceeds by the amount corresponding to (.+-.nf) frames (referred to as jitter margin or so).
The information reproducing apparatus is arranged that the reference clock, which is different from the lock synchronized with the reproduced data, is used as the address generating-use clock of the read address generating circuit 71, thereby resulting in that the fluctuation of the disk rotation system, which is contained in the reproduced signal, is absorbed. Accordingly, the high fidelity audio reproduction can be achieved without time base fluctuation. This is generally called as TBC (Time Base Correcting), which is a superior feature of the digital audio device.
However, in the information reproducing apparatus which uses the above-mentioned recordable disk, when the computer data, text data, compressed digital audio information, or image information are reproduced, unlike the reproducing of the continuous information, the number of the sector to be reproduced becomes discrete and the unrecorded area of the main information are distributed over the whole disk, thereby proposing the following problems.
FIG. 10 is a time chart showing the problem when the CD format is adapted to the recordable disk, and showing the operation wherein the disk normally rotates at a predetermined linear velocity and at the time of (t17) the temporary fluctuation in the disk rotation is occurred due to the disturbance such as a mechanical shock. Note that the following explains, without the address generation for the error correction, like FIG. 9 for the convenience' sake of the explanation.
FIG. 10 shows the reproducing operation where the recording information such as the computer-use coding data are stored over five sectors between sector address (n) through (n+4) with respect to a sector address (a) on the disk having the unique absolute address indicated by the pre-recorded information. A disk reproduced signal (b) delays by (df) with respect to corresponding respective sector head ends. The delay amount (df) is determined based on the delay due to the coding and decoding of the CIRC.
Sector addresses (n-1), (n+5), and (n+6), which correspond to the sectors other than the above-mentioned five sectors, are information unrecorded areas. The disk reproduced signal (b) is changed into a binary signal (c) by use of a comparator or other device. In the information unrecorded areas of sector addresses (n-1), (n+5), and (n+6), the disk reproduced signal (b) becomes a noise level. The corresponding areas C1 and C3 have meaningless data which contain the high frequency component. Accordingly, the PLL for generating the first clock which is synchronized with the disk reproduced signal (b) tries to follow the binary signal (c) and carries out the operation like (d).
More specifically, the axis of ordinate of FIG. 3(d) means the frequency wherein the locking range of .+-..DELTA.f1 is indicated. The reproducing clock is a high frequency in the area C1 of the information unrecorded area and the PLL pull-in operation is carried out at the time (t13) in the information recorded area C2 where the reproduction is carried out. At the time (t17), the rotating system receives a disturbance such as the mechanical shock to the information reproducing apparatus and follows the disturbance. When the area C3 is again reproduced at the time (t20), the slipping off the PLL is occurred thereby causing to generate a clock having a high frequency. Accordingly, a locking signal (e) indicative of the PLL pull-in states shows a locking state during the time period between (t12) and (t20).
When corresponding to the above-mentioned TBC operation, the first clock synchronized with the reproduced signal is used as the memory writing-use clock while the constant second clock is used as the memory reading-use clock. This results in that an address difference (f) between the write address and the read address gradually increases from the time (t10) and the address difference (f) exceeds the jitter margin of (.+-.nf) for the memory 73 at the time (t11), at this time the write address setting operation is carried out in accordance with the address set (g). Afterwards, the normal reproducing operation is carried out when the address difference falls within the jitter margin of (.+-.nf). However, at the time (t18), the address difference exceeds again the jitter margin of (.+-.nf) due to the affection of the small disturbance occurred at the time (t17), thereby carrying out the write address setting operation.
Accordingly, an error flag (h) indicative of the error corrected results corresponding to the above-mentioned reproducing example is correct at the time (t16) while the error flag (h) is in the error state at the time (t18) when the write address setting operation is carried out. Therefore, the reproducing operation having the original jitter margin can not be carried out upon reception of a small disturbance, thereby causing the decreasing of the reliablity of the reproducing operation. Note that the error flag (h) indicates the corrected results by the CIRC and is released followed by the interleave delay corresponding to one sector or more.
Further, as is clear from the above-mentioned example, the first clock generating frequency is extraordinarily higher than the normal freqency fc for the area C1 of the information unrecorded area. This presents the problem that the reliability for reading the head end of the start position to be reproduced is lowered since it takes long time to carry out the PLL pull-in operation from the time (t13) when the sector data to be reproduced are entered.